class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if (!root) return nullptr;
        if (root->val > p->val && root->val > q->val)
            return lowestCommonAncestor(root->left, p, q);
        else if (root->val < p->val && root->val < q->val)
            return lowestCommonAncestor(root->right, p, q);
        else return root;
    }
};